Recently, there have been developed vacuum cleaners in which electric powers provided to electric blowers therein can be controlled by detecting negative pressures inside the vacuum cleaners in order to improve suction forces. Further, in some vacuum cleaners, power consumptions are controlled to be reduced when suction flow rates are higher than a specific level while amounts of collected dust are low (see, for example, Japanese Patent No. 3326126).
FIG. 7 shows a graph representing an electric power and a current as a function of a suction flow rate in accordance with the power control method disclosed in Japanese Patent No. 3326126. As shown therein, the electric power represented as an effective power is reduced where the suction flow rate gets high. However, in this region, a total current is not reduced, because a reactive power is high and thus a power factor is low. This is not a favorable situation for a power company supplying the electric power. Further, in some cases, it may be needed to examine whether a current rating of the power supply system has to be reset, and thus, a reexamination of an upper limit of a current level of a current breaker in a distributor box provided for each household, a replacement of the current breaker, or an electrical service work may be required.
For example, in the United States, a maximum current of household electric appliances is set to be 12 A by the regulation. Conventionally, for a vacuum cleaner including an electric blower but not including an electric motor, a rated current of the electric blower is set to be 12 A. Further, for a vacuum cleaner including an electric blower and an electric motor attached thereto, a rated current of the electric blower and that of the electric motor are set to be 10 A and 2 A, respectively. Thus, vacuum cleaners set rated current loads within the maximum current limit.
Further, among such vacuum cleaners including an electric blower and an electric motor attached thereto, there is developed a vacuum cleaner capable of controlling the number of rotation of the electric motor for, e.g., driving a rotational brush in a nozzle used for the vacuum cleaner, in addition to a function of adjusting a suction force by controlling the electric power of the electric blower.